The need for the distributed systems has been determined by the type of business developed by companies with offices geographically distributed where the specific organizational structure promotes a decentralized business model. This paper describes the techniques and concepts of system architecture for distributed database management systems, followed by the presentation of implementation phases involved when dealing with the distributed queries across distributed systems. The goal of query optimization is to determine the most efficient way to execute a query in a distributed environment, by obtaining a lower system response time and also by minimizing the query execution time. For this, we will analyze the factors that influence the ways to execute a query and we will also review the available strategies to optimize the distributed query execution.